This invention relates to a stereo camera device and in particular to a stereo camera device suitable for being fitted with a high-resolution type image pickup device.
In recent years, a object detection device which utilizes a stereo camera to detect pedestrians, vehicles, and objects has been put to practical use. This device checks a plurality of images taken at the same time and calculates displacements (parallax differences) of a same object on each image by template matching. Based on the calculated parallax difference obtained from the above, it is possible also to calculate the positions of the object in the real space by a well-known conversion equation.
The stereo camera device of the present invention uses a pair of images photographed by two sets of image-taking means to recognize the object by calculating the distance to the object. The stereo camera device having the abovementioned function is beginning to find applications for a monitoring system to detect intrusion by suspicious individuals or any other abnormality, or for a vehicle-mounted system to support safe driving of cars.
The stereo image processing used for monitoring systems and vehicle-mounted systems is to measure distances with the application of triangulation technique to a pair of picture images of an object taken a certain distance apart from each other. Generally, such a stereo image processing device is equipped with a pair of image-taking means and a stereo image processing LSI which applies the triangulation technique to a pair of picture images outputted from the above image-taking means. This stereo image processing LSI realizes the processing by the triangulation technique in such a manner that the picture elements contained in the pair of picture images are made to overlap each other to expose displacements (parallax differences) of the same spots between the two images. For successful processing, therefore, it is ideal that no displacement other than the parallax differences should exist between the pair of images. Each image-taking means should be well adjusted in advance so that there will be no displacement in relation to optical characteristics and signal properties. Also, positional relationship between cameras must be properly determined preliminarily.
In the vehicle-mounted environment, it is necessary to realize recognition and distance measurement of a long-distance object so as to meet with application requirements, for example, for detection of vehicles, walkers, and objects located anteriorly to find out in advance how to maneuver for safety.
The measuring distance Z is calculated by triangulation technique by the following formula, where δ: parallax difference; f: focal length; and b: base-line length.Z=b·f/δ
In finding the distance, the more distant the distance is, the smaller the parallax difference δ will become. For this reason, the farther an object is located, the more significant effect the object will have to the extent that an erroneous calculation even by one pixel will greatly affect the result and lower the accuracy. In other words, in order to obtain a better accuracy in terms of distance, it is important to use a high-resolution type image pickup device, thereby enhancing resolution power for parallax difference.
However, the use of a high-resolution type image pickup device will result in an increased load on image processing. One of the known methods to suppress the load on image processing is to process only a predetermined area out of the image data that the camera has put in the storage. See, for example, Japanese Patent No. 3018920.
However, since the method described in the patent document 1 has a fixed size of image area (which hereinafter may be referred to also as “window”) predetermined as the processing area, it can process only a certain percentage of area of the picture image at any time. In detecting objects, detection of objects located at a far distance is important when driving at a high speed, while detection of objects located at short range is necessary when driving at a low speed. If a predetermined window is used disregarding such factors as speed and other driving conditions, there is a possibility that objects may not be included in the processing area and resultantly may not be detected.